NEWS ARCHIVE

PN05-40: ASTRONOMERS DETECT MOST DISTANT EXPLOSION

Scientists using the NASA Swift satellite and several ground-basedtelescopes have detected the most distant explosion yet: a gamma-ray burst from the edge of the visible Universe.

This powerful burst, probably marking the death of a massive star as it collapsed into a black hole, was detected on 4th September 2005. The burst comes from an era soon after stars and galaxies first formed, less than a billion years after the Big Bang.

"How a single star could generate so much energy as to be seen across the entire Universe remains an unanswered question," said Dr Nial Tanvir from the University of Hertfordshire, who joined with other scientists on four continents in using a multitude of telescopes to track the burst and its afterglow for days as the burst gradually faded. "The fact that we can see it may now provide us with a new tool to help understand those very earlytimes."

"This is uncharted territory," said Dr. Daniel Reichart of theUniversity of North Carolina at Chapel Hill, who spearheaded the distance measurement. "This burst smashes the old distance record by 500 million light years. We are finally starting to see the remnants of some of the oldest objects in the Universe."

To date, only one quasar has been discovered further out in theUniverse. Yet whereas quasars are supermassive black holes containing the mass of billions of stars, this burst comes from a single star.

The discovery is being heralded as a major breakthrough in the study of the early Universe. "The hunt is now on for further such bursts which we hope to be able to use as cosmic lighthouses to discover the state of the universe at a time when the first stars had only recently turned on," said Andrew Levan, another team member from the University of Hertfordshire.

Scientists measure cosmic distances via redshift, the extent to which light is "shifted" towards the red (lower energy) part of the electromagnetic spectrum during its long journey across the universe. The greater the distance, the higher the redshift.

The 4th September burst, named GRB 050904 for the date it was detected, had a redshift of 6.29, which translates to a distance of about 13 billion light years from Earth. (The Universe is thought to be 13.7 billion years old.) The previous most distant gamma-ray burst had a redshift of 4.5. The most distant quasar known is at redshift 6.4.

Swift, a joint US/UK/Italian mission, detected GRB 050904 and relayed its coordinates to scientists around the world withinminutes. Gamma-ray bursts disappear quickly, which is why Swift was designed to autonomously detect and locate bursts and notify the science community via e-mail, Web sites and even mobile phone text messages.

The team discovered the afterglow with the SOAR (Southern Observatory for Astrophysical Research) telescope atop Cerro Pachon, Chile, and soon after it was picked up by the United Kingdom Infrared Telescope in Hawaii.

Over the next several nights, these results were combined with further observations from the Gemini South telescope, also on Cerro Pachon, to calculate a redshift of greater than 6 via a light filtering technique.

Building upon all this information, a team led by Nobuyuki Kawai of the Tokyo Institute of Technology used the Subaru Observatory on Mauna Kea, Hawaii, to confirm the distance and fine-tune the redshift measurement to 6.29 via a technique called spectroscopy.

"We designed Swift to look for faint bursts coming from the edge of the Universe," said Dr. Neil Gehrels of NASA Goddard Space Flight Center, Greenbelt, Md., Swift principal investigator. "Now we've got one and it's fascinating. For the first time we can learn about individual stars from near the beginning of time. There are surely many more out there."

NOTES FOR EDITORS

REDSHIFTRedshift 2 is about 10 billion light years; redshift 5 is about 12billion light years. Star formation began about 200 million years after the Big Bang, at a redshift between 20 and 10.

SwiftSwift is a NASA mission managed by Goddard Space Flight Center inGreenbelt, Md. Mission operations are conducted by Penn State University. Swift's other national laboratories, universities, and international partners include the Los Alamos National Laboratory, Sonoma State University, the United Kingdom, and Italy. For further information, see http://grb.sonoma.edu or http://swift.gsfc.nasa.gov.

The UK role in Swift has been to provide core elements of the narrow field instruments (the X-ray telescope and the UV/Optical telescope), utilising mature technology already developed for the ESA XMM-Newton mission, and the JeT-X instrument.University of Leicester - lead role in the X-ray telescope design, focal plane camera assembly and X-ray design (using past experience from JET-X and XMM-Newton). The UK SWIFT Science DATA Centre, at Leicester, will provide an archive of all SWIFT data, with open access for the wider UK astronomical community.Mullard Space Science Laboratory, UCL the major part of the UV/Optical telescope was constructed at MSSL using designs and expertise from the XMM-Newton Optical Monitor.UK Swift website